Method and apparatus for artificial making of snow

ABSTRACT

A method for artificial making of snow by a snow making machine (1) comprising a series of nozzles (8) arranged to provide a tubular flow (2) of bulk water drops which are moved along by an inner flow (3) of feeder air, and a series of atomizing nozzles (10) arranged to provide a flow of super cooled nuclei which are created at or adjacent the outer periphery (9) of the snow making machine (1) by a series of atomizing nozzles (1) which are distributed round the snow making machine and radially outside and preferably downstream the bulk water jet nozzles (8) as seen in the flow direction, whereby there is formed a shell (5) of super cooled nuclei extending circumferentially round the flow (2) of bulk water drops, which successively, and over a relatively long way of movement provides a freezing of the drops of water in the flow (2) of bulk water drops.

The present invention generally is concerned with artificial snowmaking, and the invention more particularly relates to a method and anapparatus for making snow crystals by means of snow making machines moreeffectively, with a higher capacity and with an improved snow crystalformation than has so far been made.

When making snow by means of snow making machines water is ejectedthrough a large number of fine atomizing nozzles and is carried along bya central flow of air. For making small drops of water freeze stronglyinto frozen particles, so called "nuclei" are introduced into the flowof water drops, the so called bulk water flow. The making of snowcrystals by means of this type of snow making machine therefore mainlyfollows two successive steps:

in a first step strongly frozen water nuclei (plural form of nucleus)are created in a separate apparatus, called an atomizer;

in a second step the nuclei, thereby formed, are mixed with water dropscoming from the ordinary water jet nozzles of the snow making machine ina so called "plume" having a turbulent flow of air some distance fromthe snow making machine.

In all priorly known snow making machines only some of the water dropsare being frozen are influenced by the nuclei while the water drops arestill suspended in the air, whereas a certain part of the ejected waterdrops fall to the ground in a non-frozen or only partly frozencondition. When such non-frozen water drops frozen lying on the groundthey generally form a undesired layer of ice or an egg shell like layerof ice which, when subjected to a load, crack thereby giving off water.

For obtaining an ideal snow mixture in a snow making machine it would benecessary to provide a nuclei activation of any and all water drops inthe system, thereby transforming any liquid to ice crystals while thewater drops are still suspended in the air. To this end it is primarilynecessary:

to provide an excess production of nuclei;

that the nuclei grow to a sufficient size as to survive beyond the placeof mixing the nuclei with the water drops in the so called "plume";

that the mixing of nuclei and the water drops takes place after thewater drops have been super-cooled.

The creation of nuclei follows certain technical laws: extremely smallwater drops are formed spontaneously when the absolute humidity is fourtimes higher than the saturation humidity for a given temperature. Suchextremely small water drops freeze spontaneously and create smallice-aggregates if the temperature can be reduced to -42° C. or stillless temperature. The said small ice-aggregates grow to sufficientlylarge nuclei by the so called "Bergeron-process", which shortly meansthat the ice-aggregates will grow at the expense of the water drops ifthe ice-aggregates co-exist with the water drops in liquid form in asuper humidity saturated environment.

In priorly known snow making machines the strongly cooled nuclei used tobe injected more of less directly into the flow or air including thewater drops, in some cases from inside the curtain of ejected waterdrops. This has an effect both that the water drops which are locatedclose to the outer periphery of the flow of water drops are beingconfronted with the relatively warm ambient air, and also that thecooling energy of the nuclei is relatively quickly consumed, whereby apart of said energy gets lost in that the water drops do not get asufficiently long time to freeze to form ice crystals.

An important feature of the present invention is that the nuclei, whichact as catalysts in the freezing process, are created such as to form ashell, or a containment layer, of nuclei surrounding the core of waterdrops which are conveyed by a flow of air which is first laminary andwhich, at a distance beyond the water nozzles, is broken up and becomesturbulent. The nuclei are created at a place where the flow of air hasthe lowest speed thereby forming a containment layer which is movedalong without being broken up to any substantial degree and as far as toa place where the air flow changes from laminary to turbulent air flow.The water drops enclosed by the shell of nuclei thereby get asubstantially prolonged time for freezing to ice crystals. By formingthe snow making machine with a nose cone of a suitable streamline typethere is formed a "back zone" or a "static eddy", having practicallystill standing air at the tip of the nose cone, into which zoneextremely finely atomized water drops are ejected at a specificpressure, and whereby said extremely finely atomized particlesspontaneously freeze to extremely small ice crystals having a very lowtemperature, generally a temperature of -42° C. Such super frozen icecrystals provide the nuclei of the system. Thanks to the specific shapeof the nose cone the ambient air is sucked past the nose cone therebybringing the nuclei, thus formed, into the flow of air.

The numerical relationship between the concentration of ice aggregatesand the concentration of water drops can be controlled, and according tothe invention this is made in that the environment in which said phasescooperate can be isolated for a certain period of time, and hence allwater drops, or at least the major part thereof, can be brought to beconsumed by the growing water-nuclei.

It has also shown that a special effect can be obtained if the pressureof the nozzles forming the nuclei is brought to pulsate so that theatomized drops of water are formed in successive pulses.

It is also important to create a changed environment, namely anenvironment having a super saturated humidity, and to isolate saidenvironment from the ambient atmosphere. This made in two stages:

in a first stage the "ordinary" atomizing nozzles pulsate out the waterby a random fluctuation by a co-operation between compressed air andwater inside the collection tube of the atomizer. At each pulse thenozzles create a) the required drops of water for the growth of nucleiand b) small ice aggregates. It should be observed that it is possibleto optimize the above mentioned numerical concentration relationship byan adjustment of the relationship between air and water in thecollection tube

a closed containment layer, or a shell, is formed outside the laminarflow of the plume. The laminar adjusted shape (see FIGS. 1 and 2)provides layers of the secondary air which is introduced by the viscousborder flow which is formed by the laminar flow of air. Such a dampingprevents the air from becoming dispersed. Between the border lines B1and B2, as shown in FIGS. 1 and 2, there is consequently formed acasing, that is a containment layer, or a shell, of nuclei. The secondfeature of the invention relates to the back zone, or the static eddy Z(see FIGS. 3, 5, 6) which is present just outside the outlet of the nosecone. The air velocity is practically zero at said static eddy, and thekinetic energy of the material leaving the atomizing nozzles is low.Therefore said material stays in the containment layer thereby buildingup super frozen ice crystals.

The necessary temperature for having the water freeze spontaneously,which is a temperature of -42° C., is obtained locally in the saidstatic eddy by utilizing the specially shaped nose cone as a heatexchanger (pre-expansion) and the abrupt expansion when the materialleaves the nozzle and is thereby subjected to atmospheric conditions.

In this way it has been possible to create nuclei and to provide agrowth environment therefor, and to prevent the nuclei from co-actingwith the bulk water during the entire length of the laminar aid flow.The bulk water has got sufficient time to become cooled to thetemperature of the surrounding wet bulb before there is any mixing ofwater drops and nuclei.

The final stage of the method is the mixing of the fully grown up nucleiand the super cooled water drops. This is made by a turbulent, but stillcalm and steady mixing step which is made at the position III as shownin FIG. 2. The relationship of the pressure and the volume is changed inrelation to the distance from the outlet of the nose cone and causes abreaking up of the border layer of the nuclei shells. The remainingkinetic energy provides a complete freezing of an optimum amount of thewater particles while they are still presently suspended in the air, sothat all water drops freeze to ice and solely ice crystals are spreadand fall to the ground.

It has shown that it is of certain importance how the arrays of bulkwater nozzles are arranged. The nozzles generally are mounted on severalsuccessive water supply rings. On the one hand the nozzles should not bemounted so as to obstruct the conveyor air provided by an air fan; onthe other hand good effects are obtained if at least the nozzles of thefirst ring of nozzles, and eventually also the nozzles of two or moresuccessive nozzles rings, open slightly inside the conveyor air flow. Itis also of importance at what angles the bulk water jets are introduced.Very good effects have been obtained if the nozzles of the last ring ofbulk water nozzles, as seen in the flow direction, are mounted so as todirect their water jets at a course angle to the axis of the conveyorair flow. By mounting said nozzles accordingly there is obtained anincreased length and width of the static eddy at the mouth of the nosecone, and in addition thereto the flow or conveyor air can assist inproviding a secondary splitting up of the water drops, both receivedfrom said last ring of bulk water nozzles, and to some extent also fromthe preceding rings of bulk water nozzles.

Now the invention is to be described more in detail with reference tothe accompanying drawings.

In the drawings:

FIG. 1 very diagrammatically illustrates the method according to theinvention.

FIG. 2 illustrates more in detail the system stage comprising thecreation of a shell of nuclei.

FIG. 3 shows a detail of FIG. 2 in a larger scale.

FIG. 4 illustrates the effect of the pulsing activity while creating thenuclei.

FIG. 5 shows the air flows in and around the snow making machine.

FIG. 6 is a cross section through a portion of the injection part of thesnow making machine, and

FIG. 7 shows the shape of the nose cone of a snow making machineaccording to the invention.

FIG. 8 shows a partial cross section view of a snow making machinehaving the bulk water nozzles mounted so as to give an improved effect,and

FIG. 9 is an explanatory view of, in an enlarged scale, of the bulkwater nozzles of FIG. 8.

FIG. 1 shows a snow making machine 1 which is arranged, as known per se,to eject a tubular curtain or a bulk flow 2 of water drops which aremoved along from the snow making machine by means of an air flow 3 whichis laminarly adjacent the snow making machine 1 but which turns to aturbulent flow 4 some distance therefrom. According to the invention ashell 5 of nuclei is formed adjacent the outer periphery of the snowmaking machine, and more particularly at the back zone (static eddy) Zof the mouth or tip of the nose cone, which nuclei shell is conveyed bya flow 6 of ambient air which sweeps over and past the nose cone of thesnow making machine. It is indicated in FIG. 1 that the bulk flow 2 ofwater drops and also the shell of nuclei widen conically from the snowmaking machine, whereby the water drops of the bulk flow 2, during thelaminar part of the air flow 3, get a relatively long time for beingcooled to the existing so called "wet bulb" temperature (the temperatureof the circumferential cold wall B1, see FIGS. 2 and 3) and to becomefrozen to form ice crystals. A more complete contact between the nucleiand the water drops/ice crystals is obtained at the turbulent part 4 ofthe flow, in which all remaining water drops, or at least the major partof the still not frozen water drops, become finally frozen.

FIG. 2 shows a snow making machine according to invention having an airinlet funnel 7 in which an (not illustrated) air fan is mounted forcreating the flow 3 of air which moves off the bulk water drops, and ata later stage moves off the ice crystals, and which spreads same over acertain ground area. The snow making machine is formed with a largenumber of bulk water jet nozzles 8 for providing the flow of waterdrops, and said water jet nozzles are distributed in arrays around atubular nozzle carrier. The water jet nozzles 8 are mounted obliquelyinwards/forwards close to the outlet of the snow making machine. At thefront end of the snow making machine, and adjacent the tip of aspecially shaped nose cone 9, there is a series of atomizing nozzles 10which are mounted round the periphery of the snow making machine, andwhich are of a type providing an extremely fine atomizing of water,whereby such extremely fine atomized water drops spontaneously freeze to-42° C. when expanding downstream the atomizing nozzles 10 therebyforming the super cooled nuclei which are needed for the process. Theatomizing nozzles 10 are mounted radially outside the bulk water nozzles8 and a slight distance in front thereof, as seen in the flow direction,and as close to the mouth or tip of the nose cone 9 that the water dropsare being ejected into the static eddy Z, which is formed at thedownstream front end of the nose cone. It is important that the nosecone forms a cover which sealingly engages the periphery of the snowmaking machine so that no air can enter from behind and sweep past theatomizing nozzles 10. The injection of the finely atomized drops ofwater into the back zone (static eddy) Z is made at the phase positionwhich in FIG. 2 is marked as the static limit I. From said limit I thenuclei are moved in a laminar flow as far as to a limit II in the formof a surrounding shell 5 of super cooled nuclei. At the limit II thenuclei enter a turbulent air flow of successively increased turbulency.In the area between the limits I and II the nuclei grow at the same timeas the water drops of the bulk(water flow 2 are allowed to becomesuccessively cooled to the existing wet bulb temperature B1. In the areabetween limit II and limit III there is an increased contact between thenuclei at the surrounding shell 5, in particular from the innercircumferential limit surface B1, and the water drops of the water bulk2. The shell of nuclei cools the water drops and, concurrentlytherewith, prevents the water drops from becoming warmed up depending ona contact with ambient air 6. During the entire, rather long, way ofmovement between the limits I and III the water drops have a possibilityof freezing, thereby forming ice crystals, depending on the contact withthe nuclei, and as a consequence of said long time contact an optimumlarge amount of the water drops freeze to ice crystals. After the limitIII there is a complete turbulency whereby eventually existingnon-frozen water drops freeze to form ice crystals so that the masswhich finally falls to the ground is a practically water free masscomprising completely frozen ice crystals.

FIG. 3 shows more in detail how the water jet nozzles 8 are mountedinside the nose cone 9 and how the atomizing nozzles 10 are mounted anddirected adjacent the tip of the nose cone 9. The nose cone has such astreamline shape, as best shown in FIG. 7, that there is created astatic eddy Z at the outlet end thereof, in which zone Z the nuclei canbe formed without any disturbing influence from the flow 2 of waterdrops or from the surrounding flow 6 of ambient air.

For creating nuclei as quickly as possible and at the best possibleconditions it is advantageous to pulsate the flow of water through theatomizing nozzles 10. In FIG. 4 is illustrated how the nuclei arecreated and cool the bulk water in the above mentioned stages as far asto limits I, II and III during a cycle of pulsation, and the figureshows the changes in drop size in relation to the time, namely:

stage A, a short moment during which small super cooled ice crystals arecreated when the drops of water leave the atomizing nozzles;

stage B, in which the size of the ice crystals are built up without anychange of environmental conditions;

stage C, during which aggregates of ice crystals and water drops aresuccessively built up until the water drops are completely frozen to icecrystals.

In FIGS. 5 and 6 is illustrated how the flow of bulk water drops 2 ismoved along by the central air flow 3 of the snow making machine and howthe flow of nuclei 5 is forwarded from the static eddy Z by the flow 6of ambient air passing by, and how the drops of water successively comeinto contact with, and are mixed with the nuclei after having been movedalong by a substantially laminar flow of conveying air 3, whereas theflow of nuclei 5 form an insulating shell round the flow 2 of waterdrops.

As indicated in FIG. 7 the nose cone 9 ought to have a mouth or tipwhich, in a longitudinal cross section, is formed almost like aparabola, and which creates a static eddy Z downstream said tip of thenose cone. In said static zone Z the air speed is almost zero, and thenuclei have sufficient time for being built up to a shell 5 of nucleiextending circumferentially round the flow 2 of bulk water drops, andwhich shell is delimited interiorly by the border line B1 and exteriorlyby the border line B2 by the accompanying flow 6 of ambient air (asshown in the drawings).

As mentioned above improved effects can be obtained if the arrays ofbulk water nozzles are arranged in special radial locations and aredirected at specific angles in relation to the longitudinal direction ofthe snow making machine.

The nozzles generally are mounted on several successive water supplyrings, 8a, 8b, 8c and 8d as shown in FIG. 9. On the one hand the nozzlesshould not be mounted so as to obstruct the conveyor air 3 provided byan air fan; on the other hand good effects are obtained if at least thenozzles of the first ring 8a of nozzles, and eventually also the nozzlesof two or more successive nozzles rings 8b, 8c and 8d, open slightlyinside the outer periphery 11 of the conveyor air flow. In FIGS. 8 and 9is shown that the nozzles of the first ring 8a open radially inside theair flow 3, whereas the nozzles of the succeeding rings 8b, 8c and 8dopen closed to, or even slightly outside said air flow periphery 11.

It is also of importance at what angles the bulk water jets areintroduced. Very good effects have been obtained if the nozzles of thelast ring of bulk water 8d, as seen in the flow direction, are mountedso as to direct their water jets 12 at a rather course angle d to theaxis of the conveyor air flow 3. The angle may be e.g. 50°-75°, orpreferably 60°-70°. By mounting said nozzles 8d accordingly there isobtained an increased length and width of the static eddy Z at the mouthof the nose cone 9, and in addition thereto the flow of conveyor air canassist in providing a secondary splitting up of the water dropstherefrom.

Also the further nozzles 8a, 8b and 8c should be mounted at specificangles, the first nozzles 8a e.g. at 25°-35°, the second nozzles 8b ate.g. 30°-40°, the third nozzles 8c e.g. at 35°-45°, etc. Thereby theconveyor air flow can provide an additional splitting up of the waterdrops both received from said last ring of bulk water nozzles 8d, and tosome extent also from the preceding rings of bulk water nozzles 8a, 8band 8c.

Reference numerals

z static eddy

B1 inner border for nuclei

B2 outer border for nuclei

I limit for static stage

II limit for laminar flow

III limit for fully turbulent flow

1 snow making machine

2 flow of bulk water drops

3 feeder air flow

4 turbulent flow of nuclei

5 shell of nuclei

6 flow of ambient air

7 air inlet funnel

8 water jet nozzles

9 nose cone

10 atomizing nozzles

11 outer periphery of feeder air flow 3

12 water jet

I claim:
 1. Method for artificial making of snow by means of a snowmaking machine having an outer periphery (1) comprising a series ofnozzles (8) arranged to provide a tubularly extending flow (2) of bulkwater drops which are moved along by an inner flow (3) of feeder air,and a series of atomizing nozzles (10) arranged to provide a laminarflow of super cooled nuclei, said laminar flow having a surface whereinthe flow of nuclei is created at or adjacent the outer periphery (9) ofthe snow making machine, without being influenced by the air flow (3)conveying the flow (2) of bulk water drops, by means of a series ofatomizing nozzles (10) distributed round the snow making machine,whereby there is formed a shell (5) of super cooled nuclei extendingcircumferentially round the flow (2) of water drops, which successively,and over a relatively long way of movement provides a cooling down andfreezing of the drops of water in the flow (2) of bulk water drops. 2.Method according to claim 1, wherein the freezing to ice of the waterdrops in the flow (2) of bulk water drops is made in two stages, a firststage (I-II), in which the flow (2) of bulk water drops is brought intocontact with the surface (B1) of a said substantially laminary flow ofsuper cooled nuclei, and a second stage (II-III) in which the waterdrops are mixed with a turbulent flow of the super cooled nuclei. 3.Method according to claim 1 or 2 wherein the atomizing nozzles aremounted radially outside the bulk water jet nozzles and wherein the snowmaking machine includes a nose cone having a tip formed as a sealedcover designed so as to provide a static eddy zone (Z) at the downstreamend of the nose cone tip, in which zone Z the flow speed is almost zero,and into which zone said atomized water drops from said atomizingnozzles (1) are injected and in which the atomized water drops can besuper cooled without being influenced by the ambient flows of air (6) orwater drops (2).
 4. Method according to claim 1, wherein the flow ofwater through the atomizing nozzles (10) is pulsated, whereby the supercooled nuclei, thereby formed, get a possibility of building themselvesup to an increased volume before the cooling capacity of the nuclei isfully utilized for freezing the water drops of the flow (2) of bulkwater drops.
 5. Method according to claim 1, wherein the nose cone (9)of the snow making machine (1) is a sealed cover and is formed so as todirect a pliable flow (6) of ambient air past the nose cone (9) and sothat said ambient air flow moves the nuclei out from the snow makingmachine in the form of a shell (5) of nuclei, first having a laminaryflow over a certain length, whereby the water drops of the flow (2) ofbulk water drops get a relatively long time for being cooled down andfrozen, and thereafter, in a successively increased turbulent flow (4),the bulk water drops are being freezed completely.
 6. Apparatus formaking snow comprising a snow making machine (1) having a peripherycomprising a series of bulk water jet nozzles (8) arranged so as toprovide a conveyor air flow (3) for moving said flow (2) of bulk waterdrops forwardly, and a series of atomizing nozzles (10) arranged toprovide a flow (5) of super cooled nuclei, wherein the atomizing nozzles(10) are distributed over a ring extending round the snow making machineat or close to the periphery thereof and radially outside the series ofbulk water nozzles (8).
 7. Apparatus according to claim 6, wherein thesnow making machine is formed with a nose cone (9) having a streamlineshape and formed as a cover which sealingly engages the periphery of thesnow making machine, and in that the atomizing nozzles (10) are mountedat or adjacent the tip of the nose cone (9) and downstream the bulkwater jet nozzles (8).
 8. Apparatus according to claim 7, wherein thenose cone (9) is designed so that the downstream end thereof provides astatic eddy (Z) which is not influenced by the feeder air flow (3) forthe bulk water drops (2), and in which the flow speed is almost zero,into which zone (Z) the flow (5) of atomized (10) water drops isinjected, and in which said atomized water drops are allowed to becomesuper cooled thereby creating nuclei, and from which zone (Z) saidnuclei are forwarded by a flow (6) of ambient air in the form of acircumferentially extending shell (5) of super cooled nuclei in a flowwhich is first a laminary flow (I-II) and is thereafter turned to a flow(II-III) of successively increased turbulency.
 9. Apparatus according toclaim 6, wherein the apparatus comprises first means for ejecting acontinuous flow of water drops through the bulk water jet nozzles (8),and further means for ejecting a pulsating flow of water atomized waterdrops through the atomizing nozzles (10).
 10. Apparatus according toclaim 9, wherein the bulk water jet nozzles (8a-8d) are mounted insuccessive radial arrays, in that the nozzles (8d) of the last array ofwater jet nozzles, as seen in the flow direction, are mounted at anglesof 50°-750°, and in that the nozzles (8a-8c) of the preceding arrays ofbulk water jet nozzles are mounted at angles of 25°-45° to the flowdirection, eventually at successively increased angles for thesuccessive arrays of nozzles (FIGS. 8 and 9).